This invention relates to a method of cleaning a column while it is in service and to apparatus comprising a column that can be cleaned while it is in service. In particular, it relates to the use of nozzles mounted on the outside of the column and to a lance that slides through the nozzles and emits a fluid under high pressure into the column during its operation.
In the manufacture of hydrocarbon products, heavy hydrocarbons such as diesel oil are cracked in furnaces into a mixture of smaller molecules such as ethylene, butadiene, benzene, and propylene. This mixture of hydrocarbons is cooled with circulating oil and is separated into its various component in a vertical column. The column contains a number of horizontal baffles or trays. The trays are perforated by a large number of holes which are covered with bubble or valve caps that permit gases to move upwards and liquids to move downwards in the column. Lighter products, such as ethylene, propylene, and aromatics, exit from the top of the column while liquids exit from the bottom of the column. Products of intermediate weight can be drawn off the column at different heights.
After the column has been in operation for some time, a buildup of small granules of polymer called "popcorn" polymer occurs. Some of the popcorn polymer plugs up the holes in the trays around the bubble caps, preventing the gases and liquids from moving easily through the column. This changes the temperature profile of the column so that the various fractions of the products do not exit the column at the correct locations. Also, the mix of products produced can be altered. For example, too much gasoline can be made. In order to correct this situation, it is necessary to shut down the column and decontaminate it so that personnel can enter and remove the popcorn polymer. Removal is accomplished using high pressure water hoses, scrapers, and chisels. It can require a hundred people working for two weeks to clean a column and put it back into operation again.